Sensor assembly with hydrophobic filter

ABSTRACT

The present disclosure relates to methods and devices for reducing moisture, dust, particulate matter, and/or other contaminates entering a sensor. A sensor assembly may include a housing with an inlet flow port and an outlet flow port. The housing may define a fluid channel extending between the inlet flow port and the outlet flow port, with a sensor positioned in the housing and exposed to the fluid channel. The sensor may be configured to sense a measure related to the flow rate of a fluid flowing through the fluid channel. A hydrophobic filter may be situated in the fluid channel, sometimes upstream of the sensor. When so configured, and during operation of the sensor assembly, a fluid may pass through the inlet flow port, through the hydrophobic filter, across the sensor, and through the outlet flow port.

This application is a continuation of U.S. application Ser. No.12/729,173, entitled “SENSOR ASSEMBLY WITH HYDROPHOBIC FILTER”, filed onMar. 22, 2010, which is hereby incorporated by reference.

RELATED APPLICATION

This application is related to U.S. application Ser. No. 12/729,145,entitled “FLOW SENSOR ASSEMBLY WITH POROUS INSERT”, filed Mar. 22, 2010,which is hereby incorporated by reference.

FIELD

The present disclosure relates generally to sensors, and moreparticularly, to methods and devices for reducing moisture, dust,particulate matter and/or other contaminants in a sensor.

BACKGROUND

Sensors, such as pressure and flow sensors, are often used to sense thepressure and/or flow of a fluid (e.g. gas or liquid) in a fluid channel.Such sensors are often used in a wide variety of applications including,for example, medical applications, flight control applications,industrial process applications, combustion control applications,weather monitoring applications, as well as many others. In someinstances, moisture, dust, particulate matter, and/or other contaminantscan enter the sensor during use. Over time, such contaminants can impactthe accuracy, repeatability, functionality and/or other aspects of thesensor. For example, moisture in a sensor can increase corrosion orelectromigration in the flow sensor itself, which may impact theaccuracy, repeatability, functionality and/or other aspects of thesensor. Also, dust, particulate matter, or other contaminants canbuild-up and possibly obstruct the sensor. Therefore, there is a needfor new and improved systems and methods for reducing moisture, dust,particulate matter, and/or other contaminants from entering a sensor.

SUMMARY

The present disclosure relates generally to sensors, and moreparticularly, to methods and devices for reducing moisture, dust,particulate matter, and/or other contaminants in a sensor. In oneillustrative embodiment, a flow sensor assembly includes a housing withan inlet flow port and an outlet flow port. The housing may define afluid channel extending between the inlet flow port and the outlet flowport, with a flow sensor positioned in the housing and exposed to thefluid channel. The flow sensor may sense a measure related to the flowrate of the fluid flowing through the fluid channel. A hydrophobicfilter may be situated in or adjacent to the fluid channel, sometimesupstream of the flow sensor. When so configured, and during operation ofthe flow sensor assembly, the fluid may pass through the hydrophobicfilter and across the flow sensor. The hydrophobic filter may beconfigured to reduce moisture ingress into the flow sensor, while stillallowing fluid flow through the flow channel and past the flow sensor.While this example includes a flow sensor, it is contemplated that ahydrophobic filter may be used in conjunction with many other types ofsensors including pressure sensors, humidity sensors, temperaturesensors, or any other type of sensor that is exposed to a fluid (e.g.gas or liquid).

The preceding summary is provided to facilitate an understanding of someof the innovative features unique to the present disclosure and is notintended to be a full description. A full appreciation of the disclosurecan be gained by taking the entire specification, claims, drawings, andabstract as a whole.

BRIEF DESCRIPTION

The disclosure may be more completely understood in consideration of thefollowing detailed description of various illustrative embodiments ofthe disclosure in connection with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an illustrative flow sensor formeasuring a fluid flow rate of a fluid passing through a fluid channel;

FIG. 2 is a schematic diagram of an illustrative thermal flow sensorassembly useful for measuring the flow rate of a fluid passing through afluid channel;

FIG. 3 is a partially exploded perspective view of an illustrative flowsensor assembly that includes one or more filters;

FIG. 4 is a cross-sectional view of the illustrative flow sensorassembly of FIG. 3 including filters adjacent to both the inlet and theoutlet flow ports;

FIGS. 5 and 6 are cross-sectional views of the illustrative flow sensorassembly of FIG. 3 including a filter in only one of the inlet andoutlet flow ports;

FIGS. 7-9 are cross-sectional views of other illustrative flow sensorassemblies that include one or more filter structures.

DESCRIPTION

The following description should be read with reference to the drawingswherein like reference numerals indicate like elements throughout theseveral views. The description and drawings show several illustrativeembodiments and are not meant to be limiting in any way.

While the illustrative embodiments described below includes a flowsensor, it is contemplated that a filter may be used in conjunction withmany other types of sensors including pressure sensors, humiditysensors, temperature sensors, or any other type of sensor that isexposed to a fluid (e.g. gas or liquid).

FIG. 1 is a schematic diagram of an illustrative flow sensor 10 formeasuring a fluid flow rate of a fluid flow 14 passing through a fluidchannel 12. The term “fluid” as used herein can refer to a gas or aliquid, depending on the application. In the illustrative embodiment,the flow sensor 10 may be exposed to and/or disposed in the fluidchannel 12 to measure one or more properties of the fluid flow 14. Forexample, the flow sensor 10 may measure the mass flow and/or velocity ofthe fluid flow 14 using one or more thermal sensors (e.g. see FIG. 2),pressure sensors, acoustical sensors, optical sensors, pitot tubes,and/or any other suitable sensor or sensor combination, as desired. Insome cases, the flow sensor 10 may be a microbridge or a Microbrick™sensor assembly available from the assignee of the present application,but this is not required. Some illustrative methods and sensorconfigurations that are considered suitable for measuring the mass flowand/or velocity of the fluid flow 14 are disclosed in, for example, U.S.Pat. Nos. 4,478,076; 4,478,077; 4,501,144; 4,581,928; 4,651,564;4,683,159; 5,050,429; 6,169,965; 6,223,593; 6,234,016; 6,502,459;7,278,309; 7,513,149; and 7,647,842. It is contemplated that flow sensor10 may include any of these flow sensor configurations and methods, asdesired. It must be recognized, however, that flow sensor 10 may be anysuitable flow sensor, as desired.

In the illustrative example, the fluid channel 12 may experience a rangeof flow rates of fluid flow 14. For example, the fluid channel 12 mayinclude a high-volume fluid flow, a mid-volume fluid flow, or alow-volume fluid flow. Example fluid flow applications can include, butare not limited to, respirometers, flow meters, velocimeters, flightcontrol, industrial process stream, combustion control, weathermonitoring, as well as any other suitable fluid flow applications, asdesired.

Turning now to FIG. 2, which is a schematic diagram of an illustrativethermal flow sensor assembly for measuring the flow rate of a fluid flow14 passing through a fluid channel 12. In the illustrative embodiment,the flow sensor assembly may include one or more heater elements, suchas heater element 16, and one or more sensor elements 18 and 20, forsensing a flow rate of a fluid 28 in the fluid channel 12.

As illustrated in FIG. 2, the flow sensor assembly may also include oneor more filters 22 and/or 24 positioned in the fluid channel 12 upstreamand/or downstream of the heater element 16 and the one or more sensorelements 18 and 20. The filter(s) 22 and/or 24 may be configured toreduce moisture, dust, and/or other contaminants from the fluid flow 28passing through the flow sensor housing and/or produce a desired orpredetermined pressure drop along the fluid channel at a given flowrate. In some instances, the reduction of moisture, dust, and/or othercontaminants in the fluid flow may provide a more consistent, reliable,accurate, repeatable, and stable output of the flow sensor for a longerperiod of time due to the reduction of corrosion, electromigration,and/or contaminant build-up obstructing fluid flow in the flow sensor.

As illustrated in FIG. 2, the flow sensor assembly may include a heaterelement 16, a first sensor element 18 positioned upstream of the heaterelement 16, and a second sensor element 20 positioned downstream of theheater element 16. While the first sensor element 18 is shown asupstream of the heater element 16, and the second sensor element 20 isshown as downstream of the heater element 16, this is not meant to belimiting. It is contemplated that, in some embodiments, the fluidchannel 12 may be a bi-directional fluid channel such that, in somecases, the first sensor element 18 is downstream of the heater element16 and the second sensor element 20 is upstream of the heater element16. In some instances only one sensor element may be provided, and inother embodiments, three or more sensor elements may be provided. Insome instances, both sensor elements 18 and 20 may be positionedupstream (or downstream) of the heater element 16.

In some cases, the first sensor element 18 and the second sensor element20 may be thermally sensitive resistors that have a relatively largepositive or negative temperature coefficient, such that the resistancevaries with temperature. In some cases, the first and second sensingelements 18 and 20 may be thermistors. In some instances, the firstsensor element 18, the second sensor element 20, and any additionalsensor elements may be arranged in a Wheatstone bridge configuration,but this is not required in all embodiments.

In the example shown, when no fluid flow is present in the fluid channel12 and the heater element 16 is heated to a temperature higher than theambient temperature of the fluid in the fluid flow 28, a temperaturedistribution may be created and transmitted in a generally symmetricaldistribution about the heater element 16 to upstream sensor element 18and downstream sensor element 20. In this example, upstream sensorelement 18 and downstream sensor element 20 may sense the same orsimilar temperature (e.g. within 25 percent, 10 percent, 5 percent, 1percent, 0.001 percent, etc.). In some cases, this may produce the sameor similar output voltage in the first sensor element 18 and the secondsensor element 20.

When a fluid flow 28 is present in the fluid channel 12 and the heaterelement 16 is heated to a temperature higher than the ambienttemperature of the fluid in the fluid flow 28, the symmetricaltemperature distribution may be disturbed and the amount of disturbancemay be related to the flow rate of the fluid flow 28 in the fluidchannel 12. The flow rate of the fluid flow 28 may cause the upstreamsensor element 18 to sense a relatively cooler temperature than thedownstream sensor element 20. In other words, the flow rate of the fluidflow 28 may cause a temperature differential between the upstream sensorelement 18 and the downstream sensor element 20 that is related to theflow rate of the fluid flow 28 in the fluid channel 12. The temperaturedifferential between the upstream sensor element 18 and the downstreamsensor element 20 may result in an output voltage differential betweenthe upstream sensor element 18 and the downstream sensor element 20.

In another illustrative embodiment, the mass flow and/or velocity of thefluid flow 28 may be determined by providing a transient elevatedtemperature condition in the heater element 16, which in turn, causes atransient elevated temperature condition (e.g. heat pulse) in the fluidflow 28. When there is a non-zero flow rate in the fluid flow 28, theupstream sensor element 18 may receive a transient response later thanthe downstream sensor element 20. The flow rate of the fluid flow 28 canthen be computed using the time lag between the upstream sensor element18 and downstream sensor element 20, or between the time the heater isenergized and when the corresponding elevated temperature condition(e.g. heat pulse) is sensed by one of the sensors, such as thedownstream sensor 20.

In the illustrative embodiment, the one or more filters 22 and 24 mayreduce the amount of moisture, dust, and/or other contaminants in fluidflow 28 across the heater element 16 and sensing elements 18 and 20. Insome cases, the filters 22 and 24 may include a plurality of pores sizedto filter out and/or reduce the presence of moisture, dust, particulatematter, and/or other contaminants in the fluid flow 28 across the heaterelement 16 and sensing elements 18 and 20. In some embodiments, thefilters 22 and 24 can have a porous structure with pore sizes in therange of microns to millimeter depending on the desired filtration rateand filtration application. In some embodiments, the filters 22 and 24can have lengths in the flow direction of less than one inch, one inch,or greater than one inch, depending on the desired filtration, as wellas other factors. In some cases, the filters 22 and 24 can have the samepore size and length or, in other cases, can have different pore sizesand lengths, as desired.

As illustrated, filter 22 is positioned in the fluid channel 12 upstreamof the heater element 16 and one or more sensor elements 18 and 20, andfilter 24 is positioned in the fluid channel 12 downstream of the heaterelement 16 and one or more sensor elements 18 and 20. In someembodiments, however, it is contemplated that only one filter 22 or 24may be provide in the fluid channel 12, such as for example, only theupstream filter. It is also contemplated that multiple upstream and/ordownstream filters may be used, as desired, sometimes with differentfilter characteristics.

In one example, to reduce the introduction of dust, particulate matter,and/or other contaminants in the flow sensor, a filter 22 or 24 may beprovided upstream of the heater element 16 and one or more sensorelements 18 and 20. In another example, to reduce the introduction ofmoisture into the flow sensor, both filters 22 and 24 may be providedupstream and downstream of the heater element 16 and one or more sensorelements 18 and 20. In bi-directional flow sensor applications, forexample, both filter 22 and 24 may be provided.

In some embodiments, the filters 22 and 24 may include suitable filtermaterials to reduce moisture ingress into the flow sensor, such as,hydrophobic or hydrophobic treated material. For example, the filtermaterial may include woven fibers, such as, for example, a precisionwoven mesh, having hydrophobic treatments, non-woven fibers (e.g. felt)with hydrophobic treatment, polytetraflouride (PTFE), expandedpolytetraflouride (ePTFE), porous polymer and/or porous fiber materialwith hydrophobic treatment (e.g. sintered polymer particulates), and/orany other material that, for example, helps reduce moisture ingress in afluid flowing through the flow channel 12. Examples ePTFE materialsinclude Teflon® available from DuPont, and Gore-Tex® available from W.L.Gore & Associates and Versapore membrane available from PALL LifeSciences. Examples of hydrophobic porous materials are UHMW Polyethyleneor PE copolymers available from GenPore. An example of a precision wovenmesh with a hydrophobic treatment is Acoustex available from SAATItechand hydrophobically treated acoustic filters available from SefarFiltration Incorporated. An example of non woven fiber material withhydrophobic treatment is Gore Acoustic filter GAW102 available from W.LGore & Associates. Other materials that can be used include, forexample, foams (e.g. reticulated foams, open-cell foams), polyurethane,polyethylene (PE), nylon, polyethylene terephthalate (PET), polybutyleneterephthalate (PBT), polypropylene (PP), pressed metal, and/or any othersuitable material, as desired. Further, in some embodiments, the filtermay include materials that are untreated (non-hydrophobic). In theseembodiments, the filter materials may include, for example, wovenfibers, such as, for example, a precision woven mesh, non-woven fibers(e.g. felt), and/or any other material that, for example, helps reducemoisture ingress in a fluid flowing through the flow channel 12. Theforegoing materials are merely illustrative and it is to be understoodthat any suitable hydrophobic material or hydrophobic treated materialmay be used to reduce moisture ingress in the flow channel 12 of theflow sensor.

In some embodiments, the filters 22 and 24 may include a backing for thefilter materials, an adhesive applied to the materials for adhering tothe material to the flow channel 12, and/or other insert (e.g. plasticring, screen, etc.) for mounting the filter material to. In one example,the filter material may be mounted on a plastic ring, other insert, orbacker, and pressed or otherwise inserted into or otherwise positionedto filter fluid flow entering the flow channel 12 of the flow sensor. Inanother example, an adhesive may be applied to a surface of the filtermaterial for adhering the filter to the inside of the flow channel 12 orover a flow channel 12 port, as desired. An example backer for thefilter material may be non-woven PET. Furthermore, it is contemplatedthat any other suitable technique or material may be used to mount thefilters 22 and 24 to the flow sensor or flow sensor housing.

It is to be understood that the illustrative heater element 16 andsensing elements 18 and 20 are merely illustrative and, in someembodiments, may not be present, as desired. For example, it iscontemplated that the filters 22 and 24 may be incorporated into one ormore flow sensors (such as the flow sensors described and/or referred topreviously), pressure sensors, acoustical sensors, optical sensors,pitot tubes, and/or any other suitable sensor or sensor combination thatmay be used to sense a measure related to a fluid (e.g. gas of liquid)in fluid channel 12, as desired.

FIG. 3 is a partially exploded perspective view of an illustrative flowsensor assembly 30 that includes one or more filters 22 and/or 24. Inthe illustrative embodiment, the flow sensor assembly 30 includes anouter protective housing including a top protective cover 37 and abottom protective cover 36. As illustrated, the top protective cover 37may be inserted into a recess of the bottom protective cover 36. In sucha configuration, the top and bottom protective covers 37 and 36 mayprotect the flow sensing element (shown as 42 in FIG. 4) and any signalconditioning circuitry that may be provided in the housing. In somecases, the top protective cover 37 and the bottom protective cover 36may be formed from, for example, plastic. However, it is contemplatedthat any other suitable material may be used, as desired.

In the illustrative embodiment, the outer protective housing includingthe top protective cover 37 and the bottom protective cover 36 areformed as a composite. However, it is contemplated that the outerprotective housing can be molded in a single piece from a plastic orother suitable material according to design considerations. For example,it is contemplated that the outer protective housing may be formed byinjection molding or made by other suitable methods and materials, asdesired.

As illustrated in FIG. 3, the top protective cover 37 of the housingincludes a first flow port 32 and a second flow port 34, and helpsdefine a flow channel extending therebetween. The flow sensing elementis exposed to the fluid in the flow channel. In some cases, flow port 32may be an inlet flow port, and flow port 34 may be an outlet flow port,but this is not required. In some cases, it is contemplated that theflow sensor assembly 30 may be a bi-directional flow sensor assemblyand, in this case, either flow port 32 or flow port 34 may serve as theinlet flow port or the outlet flow port, depending on the currentdirection of the fluid flow through the flow channel.

Although not shown in FIG. 3, the flow sensor assembly 30 may includeone or more electrical leads (shown as 44 in FIG. 4) electricallyconnected to the flow sensing element 42 and extending external of theouter protective housing. In some cases, the one or more electricalleads 44 may include a metal pin or trace, however, any suitableconducting material or configuration may be used, as desired.

In some embodiments, the outer protective housing may also include oneor more mounting holes 38. As illustrated, bottom protective housing 36includes two mounting holes 38, but any suitable number of mountingholes may be used, as desired. The mounting holes 38 may be configuredto receive a fastener, such as a screw, bolt, or nail, to mount thebottom protective cover 36 to a desired surface to accommodate theparticular equipment for which the flow sensor assembly 30 may be used.It is contemplated that bottom protective cover 36 or the top protectivecover 37 may include additional mounting holes 38 or no mounting holes38, as desired.

In the illustrative embodiment, filter 22 may be inserted, pressed, orotherwise positioned in, on, or adjacent to flow port 32. Filter 24 maybe inserted, pressed, or otherwise positioned in, on, or adjacent toflow port 34. In some embodiments, the filters 22 and 24 may begenerally cylindrical in shape. However, it is contemplated that anysuitable shape may be used, depending on the shape of the port that thefilter is to be inserted. In other cases, it is contemplated that thefilters 22 and 24 may be any shape and, when inserted in the flow ports32 and 34, the filters 22 and 24 may be deformable to accommodate theshape of the flow ports 32 and 34. In some instances, the filters 22 and24 may be positioned in, on, or adjacent to flow ports 32 and 34,respectively, using an adhesive or other backing. In other instances,the filters 22 and 24 may be mounted on or formed on a backer or insertand pressed into flow ports 32 and 34, respectively. In yet otherinstances, the hydrophobic material of filters 22 and 24 can be insertedor pressed into flow ports 32 and 34, respectively, without any backeror insert.

The filters 22 and 24 can be configured to have a length in the flowdirection and/or pore density that will produce a desired orpredetermined pressure drop along the fluid channel at a given flowrate. For example, increasing the length, increasing the pore sizeand/or decreasing the pore density of the filters 22 and 24 may increasethe pressure drop through the flow channel, whereas decreasing thelength, increasing the pore size and/or increasing the pore density ofthe filters 22 and 24 may decrease the pressure drop. It is contemplatedthat any suitable length, pore size and/or pore density may be used forthe filters 22 and 24, depending on the desired pressure drop and otherconsiderations.

FIGS. 4-6 are cross-sectional views of the flow sensor assembly 30 ofFIG. 3. In the illustrative embodiment of FIG. 4, the flow sensorassembly 30 may include a flow sensing element 42 mounted on a packagesubstrate 40. The flow sensing element 42 may be configured to sense ameasure related to flow rate of a fluid flowing through in flow channel46. The package substrate 40 may include a ceramic material, however,other suitable types of material may be used, as desired.

In the illustrative embodiment, the housing of the flow sensor assembly30 may include a top housing cover 37 and a bottom housing cover 36. Asshown in FIGS. 4-6, the top housing cover 37 and bottom housing cover 36may define a cavity for receiving package substrate 40 with the flowsensing element 42 mounted thereon. In the illustrative embodiment, anupper surface of the package substrate 40, which includes the flowsensing element 42, and an inner surface of the top housing cover 37 maydefine flow channel 46 of the flow sensor assembly 30. The flow channel46 may extend from flow port 32 of the top housing cover 37, along theflow sensing element 42, and to flow port 34 of the top housing cover37. The flow channel 46 may expose the flow sensing element 42 to afluid flow.

As illustrated in FIG. 4, the flow sensor assembly 30 may include filter22 disposed in flow port 32 and/or filter 24 disposed in flow port 34.The filters 22 and 24 may help reduce the introduction of moisture,dust, particulate matter, and/or other contaminants in the fluid flowand/or control the pressure drop across flow sensing element 42. Asillustrated in FIGS. 5 and 6, only one filter 22 and 24 may be provided.As shown in FIG. 5, filter 22 is provided in flow port 32 without anyfilter provided in flow port 34. As shown in FIG. 6, filter 24 isprovided in flow port 34 without any filter in flow port 32. While onlyone filter 22 or 24 is shown in the embodiments of FIGS. 5 and 6, theflow sensor assembly may still reduce moisture, dust, particulatematter, and/or other contaminants from entering the flow sensor and/orprovide a controlled pressure drop across the flow sensing element 42.

While filters 22 and 24 are shown inserted into their respective flowports 32 and 34, this is not meant to be limiting. It is contemplatedthat filters 22 and 24 may be mounted over or provided adjacent to theirrespective flow ports 32 and 34. Further, it is contemplated that thefilters 22 and 24 can be provided in any suitable position to, forexample, help reduce moisture, dust, particulate matter, and/or othercontaminants in the fluid flow passing across the flow sensor and/orcontrol the pressure drop in the fluid flow, as desired. For example,filters 22 and 24 may be provided in the flow channel 46 between thepackage substrate 40 and inner surface of the top housing cover 37, ifdesired.

In the illustrative embodiment, flow sensor assembly 30 may include oneor more electrical leads 44 mounted to the package substrate 40. The oneor more electrical leads 44 may be configured to receive one or moresignals from the flow sensing element 42 corresponding to the sensedflow rate (and/or other parameter) of a fluid flowing through flowchannel 42, via one or more traces (not shown) provided on the packagesubstrate 40. In some cases, the one or more electrical leads 44 may bemetal, however, it is contemplated that they may be any suitableconductive material, as desired.

In some embodiments, water ingress into flow sensors employing filtersusing hydrophobic 3 micrometer ePTFE on non-woven PET backer andhydrophobic non-woven material (i.e. Gore Acoustic filter) may bereduced. For example, the weight of the flow sensors may change by lessthan 0.01% when immersed in water, indicating little or no ingress ofwater. In one example, flow sensors including filters using hydrophobic3 micrometer ePTFE membrane on non-woven PET backer was installed in afixture including 80 milliliters of water. The apparatus was shaken withten cycles for one orientation and then rotated 90 degrees, in which tenmore cycles were then performed. This was repeated for four differentorientations of the assembly. The pre-test weight and the post-testweight of the flow sensors were then compared. For the hydrophobic 3micrometer ePTFE membrane on non-woven PET backer, two examples sensorsweighed about 11.43 and 11.41 ounces. After the test, the two examplesensors weighed about 11.44 and 11.42 ounces, respectively, or both hadabout a 0.01 ounce change. For hydrophobic non-woven material (e.g.Gore-GAW1020308), the three example flow sensors had a pre-test weightof about 11.20, 11.33, and 11.48 ounces. The post-test weight of thethree example flow sensors was about 11.22, 11.34, and 11.49 ounces,respectively, or a change of about 0.02, 0.01, and 0.01 ounces,respectively.

In addition, the pressure drop was also measured for dry and wethydrophobic non-woven material. For the three example flow sensor whendry, the pressure drop was about 20.81, 22.45, and 24.18 mm H₂O for a1000 standard cubic centimeters per minute (sccm) flow rate, about16.06, 17.35, and 18.52 mm H2O for a 800 sccm flow rate, about 11.61,12.57, and 13.31 mm H2O for a 600 sccm flow rate, about 7.481, 8.113,and 8.514 sccm for a flow rate of 400 sccm, about 3.638, 3.936, and4.084 mm H2O at a flow rate of 200 sccm, about 1.664, 1.805, and 1.873mm H2O for a flow rate of 100 sccm, about 1.238, 1.348, and 1.377 mm H2Ofor a flow rate of 70 sccm, about 1.059, 1.136, and 1.166 mm H2O for aflow rate of 60 sccm, and about 0.8639, 0.9360, and 0.9660 mm H2O for aflow rate of 50 sccm.

For a wet hydrophobic non-woven material, the three example filters forthe flow sensor soaked in water for about 1 hour. The pressure drop forthe wet hydrophobic non-woven material was about 20.61, 22.29, and 23.83mm H2O for a 1000 sccm flow rate, about 15.90, 17.21, and 18.31 mm H2Ofor a 800 sccm flow rate, about 11.48, 12.43, and 13.19 mm H2O for a 600sccm flow rate, about 7.405, 8.106, and 8.471 sccm for a flow rate of400 sccm, about 3.586, 3.958, and 4.111 mm H2O at a flow rate of 200sccm, and about 1.631, 1.861, and 1.927 mm H2O for a flow rate of 100sccm.

For the hydrophobic 3 micrometer ePTFE membrane on non-woven PET backer,two examples sensors had pressure drops of about 133.0 and 136.3 mm H2Ofor a flow rate of 70 sccm, about 113.4 and 117.1 mm H2O for a flow rateof 60 sccm, and about 94.89 and 95.71 mm H2O for a flow rate of 50 sccm.As can be seen, the pressure drop of the hydrophobic non-woven filter(e.g. Gore-GAW1020308) was less than the hydrophobic 3 micrometer ePTFEmembrane on non-woven PET backer. For some applications, a maximumpressure drop of about 5 mm H2O at 200 sccm is desired. For theseapplications, the hydrophobic non-woven material (e.g. Gore-GAW1020308)had acceptable pressure drops. However, the desired maximum pressuredrop may vary depending on the application, and for some applications, ahigher pressure drop may be acceptable or desirable.

FIGS. 7-9 are cross-sectional views of other illustrative flow sensorassemblies 50, 60, and 70 similar to flow sensor 30, but has one or morealternative filters 52, 54, 62, 64, 72, and/or 74. While FIGS. 7-9 areshown having filters in the flow ports 32 and 34, it is to be understoodthat only one filter may be provided in either the upstream ordownstream flow port, and/or in another location within the channel 46,as desired.

As shown in FIG. 7, filters 52 and 54 may be inserts including an endhaving a plurality of orifices 58 configured to reduce moisture, dust,particulate matter, and/or other contaminants in the fluid flow of flowsensor 50. The size of the orifices 58 may be small enough to helpreduce water penetration because of surface tension. In the illustrativeembodiment, filter 52 and 54 may also include one or more tabs 56extending from the end of filters 52 and 54. The tabs 56 may beconfigured to be compressed by the flow ports 32 and 34 to maintain thefilters 52 and 54 in flow ports 32 and 34, respectively. Filters 52 and54 may also provide a desired pressure drop across the flow sensingelement 42 depending on the size, number and/or density of orifices 58.In the illustrative example, filters 52 and 54 have seven orifices 58.However, it is contemplated that filters 52 and 54 may have two, three,four, five, six, seven, eight, nine, ten or any other number of orifices58, as desired. In some cases, the size of orifices 58 may be on theorder of hundredths of inches. For example, the diameter (or otherdimension) of orifices 58 may be about 0.010 inches, 0.012 inches, 0.015inches, 0.018 inches, 0.020 inches, 0.030 inches, or any other size, asdesired.

As shown in FIG. 8, filters 62 and 64 may include a first end 65, asecond end 67, and a tortuous path 66 extending between the two ends 65and 67. For example, an upper end 65 of filters 62 and 64 may include anopening 61 and the bottom end 67 of filters 62 and 64 may include anopening 63. The tortuous path may extend from the opening 61 to opening63, and may extend in a helical pattern in the filters 62 and 64 to helpreduce moisture, dust, particulate matter, and/or other contaminantswhich may be present in the fluid flow from entering the flow channel 46of the flow sensor 60.

As shown in FIG. 9, flow sensor 70 may include flow ports 32 and 34having integral flow restrictors 72 and 74, respectively, to reducemoisture, dust, particulate matter, and/or other contaminants in thefluid flow of flow sensor 70. The flow restrictors 72 and 74 may includeone or more orifices 76 utilizing surface tension to reduce moisture,dust, particulate matter, and/or other contaminants. The diameter oforifices 78 may be about 0.010 inches, 0.012 inches, 0.015 inches, 0.018inches, 0.020 inches, 0.030 inches, or any other size, as desired. Inthe illustrative example, the flow restrictors 72 and 74 include fourorifices 76 having a 0.015 inch diameter, but this is just one example.

A number of illustrative implementations have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of this disclosure.Accordingly, other implementations are with the scope of the followingclaims.

What is claimed is:
 1. A sensor assembly, comprising: a housingincluding an inlet flow port and an outlet flow port, the housingdefining a fluid channel extending between the inlet flow port and theoutlet flow port; a flow sensor positioned in the housing and exposed tothe fluid channel, the flow sensor configured to sense a measure relatedto a flow rate of a fluid flowing through the fluid channel; an upstreamfilter situated in the fluid channel of the housing upstream of the flowsensor, wherein the upstream filter includes a woven mesh; and whereinduring operation of the sensor assembly, a fluid passes through theinlet flow port, through the upstream filter, past the flow sensor, andthrough the outlet flow port, the upstream filter configured to reduceingress of unwanted contaminates into the fluid channel and to the flowsensor.
 2. The sensor assembly of claim 1 further comprising adownstream filter situated in the fluid channel of the housingdownstream of the flow sensor.
 3. The sensor assembly of claim 2,wherein the downstream filter includes a hydrophobic treated material.4. The sensor assembly of claim 1, wherein the upstream filter issecured relative to the housing via a mounting insert and/or anadhesive.
 5. The sensor assembly of claim 1, wherein the flow sensorincludes a heater element and one or more sensors elements each exposedto the fluid in the fluid channel.
 6. A sensor assembly, comprising: ahousing including an inlet flow port and an outlet flow port, thehousing defining a fluid channel extending between the inlet flow portand the outlet flow port; a sensor situated in the housing and exposedto the fluid channel, the sensor configured to sense a measure relatedto a property of a fluid flowing through the fluid channel; a filtersituated in the fluid channel of the housing upstream of the sensor,wherein the filter includes a woven mesh; and wherein during operationof the sensor assembly, a fluid passes through the inlet flow port,through the filter, past the sensor, and through the outlet flow port.7. The sensor assembly of claim 6, further comprising a mounting insertfor mounting the filter relative to the housing.
 8. The sensor assemblyof claim 6, further comprising an adhesive for mounting the filterrelative to the housing.
 9. The flow sensor assembly of claim 6, whereinthe sensor includes a heater element, a first sensing element positionedupstream of the heating element, and a second sensing element positioneddownstream of the heating element.
 10. The flow sensor assembly of claim6, wherein the filter is configured to provide a predetermined pressuredrop at a given flow rate.
 11. The flow sensor assembly of claim 6,wherein the filter is an upstream filter, and the flow sensor assemblyfurther includes a downstream filter situated in the fluid channel ofthe housing downstream of the sensor.
 12. The flow sensor assembly ofclaim 11, wherein the upstream filter is positioned adjacent the inletflow port, and the downstream filter is positioned adjacent the outletflow port.
 13. A sensor assembly, comprising: a housing including afirst port and a second port; a sensor situated in the housing, thesensor in fluid communication with the first port and the second port,the sensor is configured to sense a measure related to a property of afluid; and a filter situated in the housing fluidly between the sensorand the first port.
 14. The sensor assembly of claim 13, furthercomprising another filter situated in the housing fluidly between thesensor and the second port.
 15. The sensor assembly of claim 13, whereinthe filter includes a woven mesh.
 16. The sensor assembly of claim 15,wherein the filter includes a hydrophobic woven mesh.
 17. The sensorassembly of claim 15, wherein the filter includes a hydrophobic treatedwoven mesh.
 18. The sensor assembly of claim 13, wherein the filterincludes a non-woven mesh.
 19. The sensor assembly of claim 18, whereinthe filter includes a hydrophobic non-woven mesh.
 20. The sensorassembly of claim 18, wherein the filter includes a hydrophobic treatednon-woven mesh.